Self-adhesive labelstock, a face paper for self -adhesive labelstock, a print carrier and a method for making the face paper and the print carrier for self-adhesive labelstock

ABSTRACT

A self-adhesive labelstock comprises a face paper that has an adhesive layer formed on its one side. The face paper is finished in contact over a long distance with a smooth, hot drying surface, which finishes the smoothness of the paper, such as a Yankee cylinder or a Condebelt dryer. The face paper is suitable for printing by many different printing methods.

[0001] This invention relates to a self-adhesive labelstock, a facepaper for self-adhesive labelstock, a print carrier and a method formaking the face paper and the print carrier for self-adhesivelabelstock. The self-adhesive labelstock includes the face paper, whichhas an adhesive layer formed on its one side, and with the help of thesaid adhesive layer, the paper can be attached to a desired surface.Text and/or figures can be printed on the face paper using differentprinting methods. The paper-based print carrier has the function ofbeing suitable for printing by different printing methods.

[0002] Normally, the face paper for the self-adhesive labelstock ismulticylinder-dried paper that is coated or sized and heavilycalendered. The surface deviations of the calendered paper are bothtowards and away from the structure, so the surface is relativelyuneven.

[0003] Known self-adhesive labelstocks, on which text and/or figures canbe printed, are disclosed e.g. in patents U.S. Pat. No. 5,370,420 andU.S. Pat. No. 5,543,191.

[0004] The aim of coating the base paper is to produce good printingquality. Cast coated printing papers are known e.g. from a German PatentSpecification DE-19706574 and a European Patent Specification EP-767273.

[0005] The problem with known self-adhesive labelstocks, and paper-basedprint carriers in general, is that the same product is not suitable fordifferent printing methods, and several products are needed for thedesired printing methods to be used. Especially so-called post-printing,which means printing prices and other varying information after theprinting proper, cannot be done with different printing methods on asingle label grade. The print obtained is required to have suchqualities as sharpness of characters and good contrast, which isespecially important when printing e.g. bar codes. As a consequence ofthis, several coated papers have been created in order to optimise theproperties of the coating for a certain printing method.

[0006] What is common to the demands of different printing methods isthat the standard of the properties must always remain the same and therange of variation must be narrow. However, in order to achieve a goodresult, different printing methods require the face paper to havedifferent properties. The following shows some examples of therequirements placed on paper by so-called nip printing:

[0007] The important parameters required of the paper in connection withink jet printing include:

[0008] absorption rate

[0009] formation

[0010] chemical surface properties

[0011] surface energy

[0012] roughness volume

[0013] pore volume

[0014] When using electrophotography or other dye-based methods,important parameters are e.g.:

[0015] contact surface

[0016] roughness

[0017] surface energy

[0018] formation

[0019] Using the heat transfer method, the paper is required to havee.g. the following properties:

[0020] contact surface

[0021] smoothness

[0022] formation

[0023] surface energy

[0024] The object of the invention is to present a paper suitable forprinting almost equally well by all known printing methods, whereby rawmaterials can be saved.

[0025] A print carrier according to the invention, such as a face paperfor self-adhesive labelstock, meets the requirements placed on paper bythe printing methods in such a way that good printing results areobtained with several different nip printing methods.

[0026] The main characteristics of the product according to theinvention are described in the 1st characterising part of the patentclaims below.

[0027] The invention is based on the surprising observation that papermade of chemical pulp which paper has been dried by pressing it over along distance against a smooth surface, is suitable for many printingmethods: flexographic, letterpress, offset, screen, ink jet and heattransfer printing, electrophotography, ionography and magnetography.

[0028] A print carrier according to the invention, such as a face paperfor self-adhesive labelstock, can be dried either with a Yankee Cylinderor with a Condebelt dryer. The advantage of Yankee and Condebelt dryingprocesses is that the contact surface for printing is smoother and thephysical and chemical deviations are smaller than those of amulticylinder dried, uncoated paper calendered to an equal surfacesmoothness. Paper dried with a Yankee cylinder can also be called MG(machine glazed) paper. When the fibre beating rate used for papermanufacture is optimal (SR 20-40), and when the wet web made from thisfibre is pressed against a hot smooth surface, the contact surface ofthe fibre mesh dries to match the smoothness and form of the hot smoothsurface. In the direction away from this dried contact surface into theinner layer of the paper there are pits, which arise due to the natureof the fibre mesh, the size, number and uniformity of which pits can bematched with the requirements of different printing methods. The surfaceof paper manufactured in this way can be further improved by means oflight surface sizing. An advantageous characteristic of the papersurface is its very stable cationic surface charge, which makes theresults of printing with anionic inks excellent. The dimensionalstability, smoothness and gloss of MG paper and Condelbelt paper aregood. Furthermore, the paper has a lower density and a higher porositythan calendered paper with an equally smooth surface. The smooth surfaceof the paper forms a plane, from which all roughness deviations aredownwards into the paper structure. Therefore, a self-adhesivelabelstock according to the invention can be used when printing bydifferent printing methods, whereby the need for various types oflabelstock is substantially eliminated.

[0029] The self-adhesive labelstock according to the invention and itsmanufacture are explained in greater detail in the following, withreference to the accompanying drawing, where FIG. 1 illustrates inprinciple a cross section of a self-adhesive labelstock (for purposes ofillustration, the drawing is not true to scale).

[0030] As shown in FIG. 1, the self-adhesive labelstock comprises a facepaper (1), a base paper (2), a release layer (3) and an adhesive layer(4). Text and/or figures can be printed on one surface (5) of the facepaper using different printing methods.

[0031] The face paper is uncoated paper produced by the sulphate orsulphite process, which paper may have been treated in a surface sizingunit, and whose surface is processed either with a Yankee cylinder orwith a Condebelt dryer. The grammage of the paper is 40-90 g/m².

[0032] A Yankee cylinder is a cast iron cylinder, which has a diameterof about 4-7 metres. Hot steam is fed into the Yankee cylinder at apressure of 4-7 bars in order to dry the paper. The wet paper is pressedagainst the surface of the cylinder at a nip pressure of 60-120 kN/m,which is achieved when an impression roller is pressed against theYankee cylinder in such a way that the paper remains between the Yankeecylinder and the impression roller, which are arranged to rotate. Thepaper adheres to the surface of the cylinder and dries, maintaining itsplanar dimensions. The surface of the cylinder is mirror-smooth and theside of the paper pressed against it will have similar smoothness andgloss as the cylinder surface. To enhance the drying process, thecylinder is covered with a hood and inside the hood hot air is blownonto the paper surface.

[0033] A Condebelt dryer consists of two endless rotating metal bands,which are smooth and impermeable to air, and one or more drying wiresbetween the bands. The upper band can be heated and the lower one can becooled. The width of the bands exceeds the width of the paper that isfed between them. When the wet paper is pressed between the metal bandsin such a way that one side is in contact with the heated metal band,the water starts to evaporate and it condenses on the lower metal band.To prevent the paper from getting wet again, there are usually one ortwo drying wires above the lower metal band. In the case where there aretwo wires, the surface in contact with the paper is smooth and the wireagainst the lower metal band is rough. The surface of the paper obtainedwith a Condebelt dryer is very similar to that obtained with a Yankeecylinder. Common to both methods is that the paper is dried in contactover a long distance with the same smooth metal surface. The paper's drysurface which has been in drying contact is uniformly smooth, and theroughness, i.e. the small “pits” in the surface, whose size and numberis determined by the beating rate, are beneath the smooth surface.

[0034] A surface of the paper dried in contact with one of thepreviously mentioned smooth surfaces, forms the outer surface 5 of theface paper of the self-adhesive labelstock, which surface can then beprinted.

[0035] Next, a method of producing the self-adhesive labelstock will bedescribed by way of an example, which method does not constitute arestriction to the scope of the invention.

[0036] When a self-adhesive labelstock is made, the face paper and thebase paper are brought to the production line in rolls of pre-determinedwidth and length. The face paper is first coated with a silicone layerin a roll coating unit. The layer is then polymerised and hardened at140° C. in a tubular furnace. Silicone is spread at about 1 g/m².

[0037] Next, the base paper is coated with an adhesive layer on itssiliconised side. Usually, the adhesive is a water-based dispersion,from which excess water is evaporated in a dryer. After drying, the webgoes through a dampening unit to obtain a suitable level of moisturecontent.

[0038] The face paper and the base paper are laminated together byrunning them through rollers, which press the two layers together. Theresulting laminate is then wound into a roll.

[0039] The laminate is further converted on a printing machine, whichprints the labels, die-cuts them into suitable sizes, and removes anyextra material. The printing method is determined by the characteristicsrequired of the text and/or figures on the self-adhesive labelstock, andthe application of the product. After printing proper, the label will bepost-printed, when e.g. a bar code for product and price informationetc. is added. The laminate is die-cut so that labels are formed, andthe die-cut laminate is run through two rollers opposite each other, sothat the extra material is passed after the rollers Onto one cylinderand the labels onto the other cylinder.

[0040] It is clear to one skilled in the art that many differentvariations and adaptations of the present invention fall within thescope of the claims presented below. For example, the self-adhesivelabelstock need not have a base paper, but the labels can e.g. beattached to one another. The adhesive on the back of the face paper canalso be other than a water-based dispersion, e.g. a hot-melt adhesive ora solvent-based adhesive. Likewise, a self-adhesive labelstock can referto a non-printed product, whose face paper will be printed at a laterstage, or to an at least partially printed product, which already has aprint on the face paper. Technical translation Fin-En/RM.

What is claimed is:
 1. A self-adhesive labelstock including face paper,which has an adhesive layer formed on its one side, wherein the facepaper has been finished by being in contact with a smooth, hot dryingsurface for a distance effective for finishing a face paper.
 2. Aself-adhesive labelstock as claimed in claim 1, wherein the face paperis uncoated paper.
 3. A self-adhesive labelstock as claimed in claim 1,wherein the face paper for self-adhesive labelstock includes printing.4. A self-adhesive labelstock as claimed in claim 3, wherein the facepaper for self-adhesive labelstock further includes text, figures, barcodes or combinations thereof post-printed on the face paper forself-adhesive labelstock.
 5. A self-adhesive labelstock as claimed inclaim 3, wherein printing on the face paper of self-adhesive labelstockis done by ink-jet printing, heat transfer, electrophotography or otherdye-based printing methods.
 6. A print carrier that includes a facepaper especially suitable for self-adhesive labelstock, wherein theself-adhesive labelstock is formed of high-quality chemical pulp fibreby beating at a beating rate of about SR 20 to about SR 40 and by dryingthe web intended as paper with a smooth, hot drying surface for adistance effective for finishing a smoothness of the paper, such thatthe smoothness of the paper is determined by the smooth drying surface.7. A face paper for self-adhesive labelstock, wherein the face paper hasbeen finished in with a smooth, hot drying surface effective forfinishing a smoothness of the face paper.
 8. A face paper as claimed inclaim 7, wherein the face paper is an uncoated paper.
 9. A method formaking a face paper of self-adhesive labelstock, wherein the face paperis finished in contact with a smooth, hot drying surface effective forfinishing a smoothness of the paper surface.
 10. A self-adhesivelabelstock according to claim 1, wherein the smooth, hot drying surfaceis provided by a Yankee cylinder.
 11. A self-adhesive labelstockaccording to claim 1, wherein the smooth, hot drying surface is providedby a Condebelt dryer.
 12. A self-adhesive labelstock according to claim3, wherein the printing on the face paper for self-adhesive labelstockis text.
 13. A self-adhesive labelstock according to claim 3, whereinthe printing on the face paper for the self-adhesive labelstock isfigures.
 14. A face paper for self-adhesive labelstock according toclaim 7, wherein the smooth, hot drying surface is provided by a Yankeecylinder.
 15. A face paper for self-adhesive labelstock according toclaim 7, wherein the smooth, hot drying surface is provided by aCondebelt dryer.
 16. A method for making a face paper of self-adhesivelabelstock according to claim 9, wherein the smooth, hot, drying surfaceis provided by a Yankee cylinder.
 17. A method for making a face paperof self-adhesive labelstock according to claim 9, wherein the smooth,hot drying surface is provided by a Condebelt dryer.